Subterranean filters, also known as “sand screens” or “wellscreens,” have been used in the petroleum industry for years to remove particulates from production fluids. The wellscreens have a perforated inner pipe and at least one porous filter layer wrapped around and secured to the pipe. Typically, the wellscreens is deployed on a production string, produced fluid passes through the filter layer and into the perforated pipe to be produced to the surface.
One type of wellscreen is a wire-wrapped screen. The two typical types of wire-wrapped screens include slip-on screens and direct-wrap screens. A slip-on screen is manufactured by wrapping a screen jacket on a precisely machined mandrel. Then, the jacket is later slipped on a base pipe and the end of the jacket is attached to the base pipe, typically by welding. An example of how one type of slip-on screen is manufactured by heating and shrink fitting is disclosed in U.S. Pat. No. 7,690,097.
The slip-on screen may allow for precise slots to be constructed, but the screen is inherently weaker than a direct-wrap screen. Discrepancies in the slip-on screen, such as variations in the spacing between the screen jacket and the base pipe, can be problematic. For example, differential pressure usually exists across the slip-on screen when in service, and sufficient differential pressure can cause the wires and the rods to bend inwardly into contact with the base pipe. Such a collapse will result in a shifting of the coils of wire forming the screen and reduce or destroy its ability to serve its intended purpose.
The direct-wrap screen is constructed by wrapping the screen directly on the perforated base pipe. As expected, this results in a stronger screen because any annulus between the screen jacket and the base pipe is eliminated. FIGS. 1A-1B show an apparatus 5 for constructing a wire-wrapped screen in place directly on a base pipe 10. Spaced around the outside of the base pipe 10, a number of rods 12 extend along the pipe's outside surface. The apparatus 5 wraps the wire 14 around the pipe 10 and the rods 12 to form a screen jacket. A drum (not shown) and other wire feeding components known in the art feed the wire 14 as it is being wrapped, and these components usually hold the wire in tension to bend around the pipe 10 and the rods 12.
To wrap the wire 14, the pipe 10 and rods 12 are typically rotated relative to the apparatus 5. At the same time, the pipe 10 and rods 12 are moved longitudinally at a speed that provides a desired spacing between the adjacent coils of wire 14. This spacing is commonly referred to as the “slot.” Alternatively, the apparatus 5 can be moved longitudinally along the pipe 10 and rods 12 as they rotate.
A welding electrode 16 engages the wire 14 as it is wrapped on the rods 12 and provides a welding current that fuses the wire 14 and the rods 12. The welding electrode 16 is disc-shaped and rolls along the wire 14. To complete the circuit for welding, the rods 12 are grounded ahead of the wrapped wire 14 using a ground electrode assembly 18.
The ground electrode assembly 18 includes a plurality of contact assemblies 20 and a mounting plate 28. Each contact assembly 20 includes a contact 22 and a housing 24. Proper alignment and contact is needed for good welding. Moreover, optical sensors, controls, and the like are used to ensure that proper spacing is maintained between wraps of the wire 14 and that the wire 14 is extruded properly.
Some wire-wrapped screens have long sections of wrapping along the base pipe 10. For other implementations, separate sections of screen are sometimes applied to a single base pipe at various intervals. One example of a wire-wrapped screen having multiple sections is the Mazeflo™ completion screen available from Exxon Mobil Corporation and disclosed in U.S. Pat. No. 7,464,752. (MAZEFLO is a trademark of Exxon Mobil Corporation.) These screens are sand screens having redundant sand control and baffled compartments. These screens isolates mechanical failure of the screen to the local compartments of the device's maze sections, while allowing continued hydrocarbon flow through the undamaged sections. The flow paths are offset so that the flow makes turns to redistribute the incoming flow momentum.
When manufacturing a wire-wrapped screen having separate screen sections, the wire wrapping process has to be stopped for each new screen section so ends of the screen section can be affixed to the base pipe. This is done using welds, or end rings can be inserted over the pipe before the next section of screen can be completed. Thus, a given section of wire wrapping has to be completed on the base pipe, and the base pipe must be removed from the wrapping apparatus so the end of the screen section can be secured to the base pipe before wrapping can proceed with the next screen section. This process is repeated until all the screen sections are completed on the base pipe. As will be appreciated, this form of manufacture for a wire-wrapped screen with multiple sections is time consuming and very costly.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.